Just to add...you have a good idea of how to pause and react to dialogue, without saying anything. Even your dead pan face is a good indication of how you're feeling. I really got that. Some people do too much with their faces and it makes them look far less real and a lot more hammy than they would if the scenario was being played out in real life. However, you add enough to it to make it funnier than a real life scenario. I think you could excell at the sarcastic reactions to situations.
You know how a dog will tilt its head slightly and use their eyes to let you know they're listening? They don't have to speak, you just know what they're thinking and, therefore, what they might be 'saying'.
That's exactly what I'm talking about. Sometimes, you have to get the physical responses right before you start spouting the words. People pause far more in real life and it's important to try to breathe as naturally as you would in reality to try to emulate a natural response.
So far, although it's only a short piece, I'm impressed with your delivery.